# [R] Differential equations

Thomas Petzoldt thpe at simecol.de
Sun Feb 26 12:48:06 CET 2017

```Hi,

yes, the suggestion of Peter Dalgaard is correct, and it can also be
done using the "event" mechanism of deSolve, see:

library("deSolve")
?events

... or the slides from our talk given at useR-2011

http://desolve.r-forge.r-project.org/slides/petz_soet2011.pdf

... or the tutorial from L.A.

http://desolve.r-forge.r-project.org/user2014/tutorial.pdf

Thomas Petzoldt

http://desolve.r-forge.r-project.org
https://stat.ethz.ch/mailman/listinfo/r-sig-dynamic-models

Am 08.02.2017 um 16:19 schrieb peter dalgaard:
> It's been a while, but I think I have gotten through this sort of situation by splitting the integration into intervals, i.e., you run from t=0 to t=20 witn initial condition c(100,0), yielding a value c(y1,y2), then you run from 20 to 40 with initial condition c(y1+100, y2), etc.
>
> -pd
>
> On 08 Feb 2017, at 11:10 , Fanny Gallais <gallais.fanny at gmail.com> wrote:
>
>> Hi,
>>
>> I'm working on a system of 2 differential equations. My initial condition
>> (t=0) is c(100,0) and i'm using lsoda function (from package deSolve) to
>> solve it.
>> My system reprensents the evoution of drug concentration in two
>> compartments throug time. Problem is I would like to model a repeated drug
>> administration. That is to say, not only 100 at t=0 but also at t=20,40,...
>> I can't find a solution to do so. I tried adding "100" to the first
>> differential equation at the times of interest but it doesn't work. Do you
>> have any idea?
>>
>> Thank you
>> F.G.
>>
>> 	[[alternative HTML version deleted]]
>>
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